Basic elements are
supported but it is enough to start working on your projects.

<library_images>

<library_materials>

<library_effects>
<diffuse><color>
or <diffuse><texture> (jpg or png)

<library_geometries>

<float_array> with positions, normals and texture
coordinates

<triangles material ...>

<library_nodes>

<library_visual_scenes>
instances

<matrix>

Tested successfully
with Google Earth models available on the Google 3D Warehouse. Support
for collada files from other origins is foreseen in a near future (3dsMax,
DazStudio).

The export from Blender
gives already good results if you use triangles and baked matrices options.

To get the .dae file:
open the model in Google Sketch Up, export to Google Earth, then unzip
the .kmz. You will get a .kml file which is used to position the model
on earth, the geometry (.dae) will be available in a subdirectoty called
models.

Note: the architecture
model shown has been developed in house and does not belong to the Google
3D Warehouse.

See the precision
of models exported to Collada from other formats. In this case, Google
SketchUp has been used to import a .3ds file and export it to Collada
(.dae).